This application claims the priority of German Application No. 10 2005 026 066.7 filed Jun. 7, 2005, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method of limiting, in a first operating condition, a torque provided by a motor vehicle internal-combustion engine, in which the first operating condition, as a result of an operation of a motor vehicle brake, when a torque of the internal-combustion engine is simultaneously demanded by a driver's intention indicator, differs from a second operating condition when the brake is not operated. The present invention also relates to a control device of a motor vehicle internal-combustion engine which, in such an operating condition, limits the torque from the internal-combustion engine, and to a computer program and a control device storage medium.
For achieving maximum acceleration when the vehicle is started from a stopped condition, its transmission line may be distorted by a simultaneously occurring demand of a high torque by way of the driver's intention indicator and a holding of the motor vehicle by operating the brake. Torque therefore does not first have to be built up during a start but already built-up torque is first compensated by the braking intervention and, when the brake is released, can accelerate the motor vehicle without any delay.
It is understood that such a distortion, which is also called “stalling”, in principle, has a wear-promoting effect. Thus, the torque which was possibly applied at a high rotational speed with a full-load of the internal-combustion engine, during the stalling, has to be dissipated by frictional work between the tires and the road or in the drive train itself. The frictional heat released in this process is a result of the product of the power generated by the internal-combustion engine, which may be in the three-digit kilowatt range, and of the time. In the case of stalled driving wheels, only frictional connections of the drive train, thus, particularly a wet clutch or a dry clutch or a hydraulic torque converter, can be used for converting the engine power to frictional heat.
These observations indicate the necessity of protecting these components from unacceptably high mechanical and thermal stress during the stalling by limiting the power of the internal-combustion engine which can take place by limiting its rotational speed and/or its torque.
In this context, it is customary to limit the torque by a limitation of the charging of combustion chambers of the internal-combustion with air or air-fuel mixture. In the case of motor vehicles with an electronically operated throttle valve (e-gas), this normally takes place by taking back, or decreasing, the throttle valve opening angle. As a result, however, the reaction time of the motor vehicle, or of the drive train also increases after a releasing of the brake and a resulting opening of the throttle valve. This is caused by, among other things, the inertia of the air mass flowing into the combustion chambers or of the inflowing mixture. The acceleration of the inert air mass delays the buildup of the torque. The full engine torque is therefore not immediately available after the releasing of the brake and the vehicle does not accelerate optimally.
In the case of turbo-engines, the charging in the stalled condition, as an alternative or in addition, is reduced by a reduction of the charge pressure. This has the disadvantage that the charge pressure first has to rise again after the releasing of the brake. The full engine torque is not available during the time required for this purpose.
It is also known to limit the maximal stalling time, thus the maximal duration of the stalling, in order not to overload the clutch. When the maximal stalling time is exceeded, for example, the signal of the driver's intention indicator can be ignored, so that, in the extreme case, the internal-combustion engine can continue to be operated in the normal idling mode. In order to have greater degrees of freedom when selecting the starting point in time, it is naturally desirable to be able to utilize a maximal stalling time which is as long as possible.
In principle, particularly with respect to sportscars, one wants to achieve a spontaneous and maximal acceleration by stalling. The described protective measures, thus a taking back, or reducing of torques, a slow buildup of torques, long reaction times, low starting powers with a low starting torque and drastic limitations of the stalling time reduce the acceptance and impair the subjectively sensed vehicle handling.
In view of the foregoing, an object of the present invention is to provide a method, a control device, a computer program and/or a storage medium by way of which the diverging demands of a component protection and a maximizing of the acceleration by a preceding stalling can be met in a better fashion.
In a method, this object has been achieved in that the limitation takes place at least partially by way of a controlled reduction of an advance angle efficiency in a first operating condition in comparison to the second operating condition.
Furthermore, the foregoing object has been achieved by a control device which reduces an advance angle efficiency in the first operating condition in comparison to the second operating condition.
With a view to the computer program and the storage medium, the solution has been achieved by programming the computer program for the application of the process, and/or in by storing the computer program on the storage medium.
The advance angle efficiency is the quotient of the torque occurring at a certain advance angle in the numerator and of the maximal torque in the denominator which occurs in the case of an optimal advance angle.
The foregoing object is in each case achieved completely by the following characteristics. The change of the advance angle efficiency can take place from one ignition to the next which, in a six-cylinder four-stroke internal-combustion engine, corresponds to a crankshaft angle of 120°. Within one operating cycle, thus, within an angle-of-rotation range of 720°, all cylinders can be switched over from the reduced advance angle efficiency to an optimal advance angle efficiency, so that in the case of 3,600 rotations per minute, used as an example, the full torque is built up within one thirtieth ( 1/30) of a second, so as to feel like a sudden buildup in the subjective perception of a human being.
With respect to charge interventions, the torque buildup takes longer because the combustion chambers operated with a reduced charge have to be newly charged in a first operating cycle before the charges can be ignited in a second operating cycle. Furthermore, the inert air mass first has to be accelerated from out of the suction pipe in the direction of the combustion chambers, which results in additional delays.
In turbo-engines, the time required for the torque buildup increases significantly more because exhaust gases of an increased charge reach the turbocharger first and have to increase its rotational turbine speed to achieve a higher charge pressure and therefore a further increase of the charge.
The present invention will therefore maximally exhibit its advantages in the case of engines having an exhaust gas turbocharger if the torque is reduced only by way of ignition interventions. When the brake is released, the full charge pressure will then be present because, in the ideal case, the air mass flow through the internal-combustion engine is not limited during the stalling and the charge pressure is therefore not reduced.
With respect to further developments of the inventive method, the impairment of the advance angle efficiency preferably takes place by reduction of the angular distance between the ignitions and an upper dead center of a piston movement of the internal-combustion engine.
If the advance angle efficiency is placed over the advance angle, a maximum will occur at the optimal advance angle. In principle, a reduction of the torque can therefore be achieved by an early ignition; that is, an ignition (early adjustment) taking place at a larger distance from the upper dead center; or by an ignition (late adjustment) taking place correspondingly closer to the upper dead center. However, in the case of an early adjustment, damage may occur at the spark plugs or at the internal-combustion engine as a result of so-called knocking combustions. The late adjustment has the additional advantage that the exhaust gas temperature rises, which increases the thermodynamic efficiency of the turbine in the case of turbo-engines.
It is also preferred that, in a supplementary manner, the limitation takes place by limiting charges of combustion chambers of the internal-combustion engine.
As a result of this combination, particularly in the case of internal-combustion engines having an exhaust gas turbocharger, a high charge pressure and thus a high starting power can be achieved when the brake is released, because the air mass flow is reduced only as little as required during the stalling. In addition, such a measure may be used for a possibly required limitation of the exhaust gas temperature for protecting components of the exhaust system and for limiting pollutant emissions during the stalling.
Another currently preferred embodiment provides that a torque loss resulting from the reduction of the advance angle efficiency is gradually reduced in the first operating condition, while a torque loss resulting from the limitation of charges is gradually increased in the first operating condition. By this measure, a constant transition can be initiated from an excessively long stalling into an operating condition in which the component protection has to again receive a higher priority than a maximal starting acceleration. When the charge is limited, the exhaust gas temperature, for example, will fall.
As an alternative, a torque loss resulting from the limitation of charges is preferably gradually reduced in the first operating condition, while a torque loss resulting from the reduction of the advance angle efficiency is gradually increased in the first operating condition. As a result, an advance angle torque reserve is gradually built up at the expense of a charge torque reserve, in which case also a rise of the exhaust gas temperature is delayed which is triggered by the late adjustment of the ignition. This reduces the thermal stressing of the components situated in the hot exhaust gas scaled to a certain stalling time and permits a lengthening of the maximally acceptable stalling time.
In this case, it is preferred that, after the expiration of a definable maximal time duration, a change takes place to the other alternative, in order again assign a higher priority to the component protection, if required. The two alternatives can therefore also be combined so that the advance angle torque reserve first increases and, if required, is then reduced again.
It is also preferred that the limitation will take place only if a driving speed of the motor vehicle is lower than a driving speed threshold value. Consequently, the reduction of the torque and of the power remains limited, for example, to the vehicle stoppage or low speeds. The dynamics of the vehicle movement are thereby prevented from being impaired at higher speeds when, for example, a certain roll steer effect of the vehicle is to be caused by a simultaneous braking and accelerating.
Additionally, a limitation of a rotational speed of the internal-combustion engine to a maximal value preferably takes place in the first condition. This measure, on the one hand, limits the power to be converted to heat during the stoppage. Simultaneously, a rotational speed reserve still occurs when the brakes are released, so that the optimal starting acceleration does not have to be interrupted early because of a required ratio transformation in the gear change box.